Diaphragm mounting for loud-speakers



S pi- 3, 1929- l. s. BOBROVSKY 1,726,52

DIAPHRAGM MOUNTING FOR LOUD SPEAKERS I Filed Jul 7, 1927 2 Sheets-$heet 1 I M Z i 1N TOR 160R OBROVSKY BY ATTORNEY Sept 3, 1929.

l. s. BOBROVSKY 1,726,524

DIAPHRAGM moumme FOR LOUD SPEAKERS Filed July '7, 1927 2 Sheets-Sheet 2 i 1 mm INVENTOR IGOR 5. BOBROVSKY BY a 9 ATTORNEY Patented Sept. '3, 1929.

v "UNITED STATES PATENT OFFICE.

IGOR S. BOBROVSKY, OF ROCHESTER, NEW YORK, ASSIGNOR TO UNITED BADId con.-

IORATION, F BOQHESTER, NEW

YORK, A CORPQRATION OF NEW YORK.

DIAPHRAGM Mom 'rmcr FOR. LOUD-SPEAKERS.

Application filed July 7,

- This invention relates to loud speaker construction and more particularly to an arrangement for establishing a Connection betweenthe periphery of the diaphragm and 5 the face plate of acabinetwithin which the speaker may be enclosed.

It is anobject of this invention to provlde an arrangement particularly adaptedfor use' with relatively small diaphragms such as a 1 0 cone not substantially exceeding 7" 1n diameter, which will permit free and unrestricted motion of the pehiphery of the diaphragm through the relatively large amplitudes of motion required to obtain low frequency re sponse from such a diaphragm. It is a further object of this invention to provide such an arrangement which will permit such amplitudes of motion while at the same time exercising substantially no restraint and substantially no restoring force upon the periphery of the diaphragm.

It is a further object of this invention to provide a construction which is relatively simple and economical to manufacture and in WhlCh the necessary operations in assembling the speaker are reduced to a m1n1- mum in order to facilitate the manufacture of a high quality loud speaker which may be sold to the public at a relatively low price.

Still other objects and advantages of myin-vvention will tion. v

The features of novelty which I believe to be characteristic of my invention are set forth with particularity in the appended claims.

be apparent from the specifica- My invention itself, however, both as toit-sfundamental principles and as to its particular embodiments wilLbest be understood by reference to the specification and accompany 1927. Serial No. 203,956.

one form of complete speaker according to my invention, and

Figures 8 and 9 are similar views of a modified form thereof.

In the development of sound re roducing apparatus of the direct-acting diaphragm type adapted to reproduce speech and music, it was discovered that it is impossible to provide good quality of reproduction with such devices operating in free and unconfined air in case the diaphragm is substantially less than nine inches in diameter. It has been found that ingeneral, the smaller'the diaphragm, the less will be the low frequency response, and that the smallest permissible size for satisfactory low frequency response is nine inches. I

.It'has further been found, however, that if, instead of operating in free and unconfined air, the diaphragm be inclosed within a cabinet .and only one side exposed to unconfined air, and if moreover, the amplitude of mkption be increased as the size of thedia- P produce satisfactory low frequency response with diaphra'gms of a size previously regarded as totally impossible of use.

It is not known that loss of low frequency response will occur in such devices, unless precautions are taken to prevent the slip pagerof airaround the edge of the diaphragm, and to prevent the. sound waves produced from the back of the diaphragm reaching the spaceat the front of the diaphragm across the edge thereof. For this purpose the ed e of the diaphragm is at. tached tothe cahinet by a rim. of freely fiexible and inelastic material in a manner to completely close any path from the back of the diaphragm to the front thereof around the edge of the diaphragm. In order to prevent any restraint. on the motion of the pe- 'riphery of the diaphragm and. to prevent the rim from exerting any restoring force on the diaphragm which would tend to hinthrough the relatively der its free vibration, large am litudes required, it has been usual to provi e-such a rim in the form of a strip or strips of soft kid joined to ether to form an annulus having its inner e ge secured to the periphery of the diaphragm, and its outer edge secured to 151101111161 face, of the ragm is decreased, then it is possible tocabinet as by a holding ring,-or by gluing the periphery of the rim to the edge of the face plate.

Such arrangements have not been entirely satisfactory, for the reason that it has been difficult to arrange the rim in the desired manner, particularly when the cone is mounted upon a face plate forming the front of a cabinet. In order to minimize the expense of the cabinet, such cabinets are usually made as small as possible, afl'ording relatively small clearance at certain points between the diaphragm and the inside of the cabinet, and making it difficult to attach the diaphragm to the inner side of the face plate.

In case of diaphragmswhich are supported at the periphery, it is difficult to obtain a uniform tension on the rim around the periphery, with the result that the diaphragm tends to vibrate asymmetrically with consequent distortion of its response characteristicz'in the case of a diaphragm supported entirely at its apex and driven thereby, it

has been found'diflicult to obtain the proper amount .of slack in the rim at all points thereof, due to the constricted space in which is was necessary to operate while establishing a connection between the rim and the face plate to prevent the slippage of air around the edges of the diaphragm.

In accordance with my invention, I eliminate the necessity of working within the constricted space in establishing this connection, by providing a chassis including a face plate, and under certain conditions, a base plate. The diaphragm is attached to the face plate, and under certain conditions the driving unit is mounted upon the base plate, forming a complete chassis which is mounted within the cabinet as a unit.

The attachment of the diaphragm to the face plate is greatly simplified according to my invention, so that one operation which may be carried out in a small period of time, produces the same result which formerly required considerable time. At the same time, the diaphragm is arranged so that it may be placed-under any degree of radial tension cured. In order to secure the rim of the diaphragm to the face plate, it is only necessary to fold the outer edge of the rim over the outer edge of the flared flange while the diaphragm is positioned at the desired point,

with reference to the opening in the face plate. An elastic member, such as a rubber band, may then be stretched and slipped over the rim to secure the rim temporarily in the desired position. Since rubber and similar substances tend to deteriorate, I prefer to supplement the elastic band with a permanent tensioned'member such as a string, wire or the like, which may be passed two or three times around the rim, drawn tight and securely fastened. If it is desired to tension the diaphragm radially, the diaphragm may be placed in position, the fastening members placed around the rim as described, and the outer periphery of the rim pulled radially at various points, thereby increasing the radial tension on the rim. Since the engagement between the rim and the flange is purely frictional, the mounting is selfadjusting as to the tension and the rim will tend to creep slowly until a substantially uniform tension is obtained at all points. If the tension is too great, it is only necessary to pull the inner periphery of the rim toward the center, when it will be found that the rim will creep under the fastening. In this manner, the rim may be adjusted so as to have any desired degree of tension or slack,- without disassembling the apparatus.

By the above procedure,-it will be found that it is a relatively simple matter to arrange the mounting so that amplitudes of movement of the diaphragm as large as one quarter of an inch may be obtained. Of course, such amplitudes are far beyond any amplitude required in operation, but in case the diaphragm is adjusted to have such free amplitude of motion, it will .be apparent that the normal amplitudes of motion in operation are well Within the limits of free vibration of the diaphragm.

Referring now more particularly to Figures 1 and 2, I have shown the preferred form of my invention as embodied in a loud speaker adapted to be built in as an integral part of a radio receiver. In this figure, ldesignates a conical diaphragm, such as paper or the like, provided with an annular flange or rim 2 of freely flexible and inelastic material such as soft kid. A face plate 3 is provided preferably of metal having an aperture 4 therein,

provided :with an inturned flange v5 preferably reversely bent and flared outwardly as shown. The face plate may conveniently be made by a stamping from a sheet of metal of the requisite thickness, the stamping being so carried out as to provide a circular flange extending inwardly which flange may be flared r by an appropriate tool. If the flange has sharp edges, they should be smoothed ofi to 7 prevent cutting the kid.

In order to secure the rim against the flange, it is only necessary to reversely bend the rim 2 over the outer side of the flange 5, and place a suitable elastic band 7 in position as shown. The band 7 forms a tempo upon the diaphragm, the outer edge of the rim may be grasped and'pulled at suitable points around the periphery, in which case the radial tension will be increased, or the inner edge of the rim may be similarly pulled, in which case the tension will be decreased. In an event, it will be noted that the pressure of the tension member upon the rim serves to hold it yieldingly in position, so that in case of excessive pull at any point, the rim will tend to creep and thereby eliminate the excessive tension.

Referring now more particularly to Figures 3 and 4, in which I have shown my invention embodied in what I term a table model, I prefer to provide a base plate 10 which may conveniently be made of metal suitably secured to the face plate 3 and having 1 a portion cut away to permit freeaccess to the bottom of the diaphragm-mount, and having an upwardly offset portion 11 upon which may be mounted a drivin unit 12 of any desired construction, but pref erably of the type shown and claimed in my copendlng application entitled Loud speakerdriving motor, Serial Number 202,213, filed June 29, 1927, which is s0 arranged as to carry and support the entire L nuts 9 and 9 weight of the diaphragm by means of a preferably aluminum cup 8 held in position by upon the end of the driving rod 13 attached to ratio arm 14, which is con- I structed and arranged as to carry the entire weight of the driving rod 13 and the diaphragm 1. The ratio arm or motion multiplying lever 14 is driven by means of a. connection 15 to a suitable armature 16 mounted upon a permanent magnet '17 which, in

turn, is carried by a suitable bracket 18 secured to the upwardly extending portion 11 of the base plate 10. t

The arrangement shown in Figure 4 constitutes thecomplete chassis of the loud speaker, which maybe mounted as a single unit within and the face a suitable ornamental cabinet 20, and se-' cured therein by suitable bolts.

The cabinet may be of any desired shape, plate may be correspondin 1y Y shaped, but in any event, the front of the ca i- E 55 net will be provided with an opening 21 corresponding with the opening 4 to permit the free emission of sound waves from the front of the diaphra so'und wavesfrom the back of the diaphragm cannot gm. Care must be taken to mount the face plate 3 flush against the in side of the front wall of the cabinet-so that pass around the edge of the face plate solid back covered with sound absorbing may terial, or with a wire screen or grill, similarly covered.

For the sake of economy in the case of the so-called built-in speakers shown in Fi ures 1 and 2, in which the entire speaker is concealed in the cabinet of the radio receiver, I prefer to use a relatively simple and inexpensive cabinet such as shown in Figure 7. In this arrangement, the method of assembly is slightly different from that described with reference to the arrangements of Figures 3, 4, 8 and 9. In the case of built-in speakers, the base plate 10 is omitted, and the face plate 3 forms the face of the cabinet. In assembling this arrangement, the diaphragm is mounted on face plate 3 as described, and the latter is then screwed to the front of box frame 25. The driving unit is then placed in proper position within the frame and securely bolted therein, after which the diaphragm is secured to the supporting and driving rod 13. The back of the box is then placed in position as described with reference to Figure 9.

Whilethe arrangements according to my invention are particularly useful in the case of a small cone as described, it is clear that they are also useful in the case of large cones or other diaphragms, and that my invention is not limited to use with the cones shown.

While I have shown and described certain preferred embodiments of my invention, it will be understood that modifications and changes may be made without departing from the spirit and scope thereof, as will be understood by those skilled in the art.

I cla1m: 1. In a loud speaker, in combination, a diaphragm, an annular rim of freely flexible and melastic material secured thereto, a face plate having an aperture therein to permit free emlsslon of sound waves from one side of said diaphragm, said face plate having an inward ly extending ortion at said aperture and said annular rim being yieldingl secured against the outer side of said inwar y extending portion.

2. In a loud speaker, in combination, a diaphragm, an annular rim of freely flexible and inelastic material secured thereto, a face plate having an aperture therein to permit free emission of sound waves, from one side of said diaphragm, said face plate having an inwardly extending flared portion at said aperture, said annular rim being reversely bent around maintain said rim the edge of said flared portion, and a tendiaphragm, said face plate having an integral inwardly extending flared portion at said aperture, said rim being reversely bent around the edge of said flared portion and a tensioned member disposed around said rim to maintain said rim yieldingly in position on said flared portion.

4. In a loud speaker, in combination, a diaphragm, an annular rim of freely flexible and inelastic material secured thereto, a metal face plate having an aperture therein to permit free emission of sound waves from one side of said diaphragm, said face plate having an integral inwardly extending flared flange at said aperture, said rim being reversely bent, around the edge of said flared flange and means for yieldingly securing said rim against the outer edge of said flange.

5. In a loud speaker, in combination, a chassis comprising a plate having a horizon? tal base portion and a vertical face portion, said face portion having an aperture therein to permit free emission of sound Waves therethrough, and having a rim-supporting portion in the form of a cylindrical face,' ,a 'diaportion, said face portion having an aperture therein to permit free emission of sound waves therethrough, and havlng a rlm-supporting portion in the form of a cylindrical trough, a diaphragm having anannular rim of freely flexible and inelastic material, driving mechanism arranged to support and drive said diaphragm positioned on said base portion, said rim being yieldably connected to the exterior of said trough to prevent slippage of air around the edge of said diaphragm.

8. In a loud speaker, in combination, a chassis comprising a metal plate having a horizontal base portion and a vertical face portion, said face portion having an aperture therein to permit free emission of sound waves, therethrough, said face plate having an integral inwardly extending flared flange at said aperture, a diaphragm having an ani nular rim of freely flexible and inelastic material, driving mechanism arranged to support and drive said diaphragm positioned on said base portion, said rim being reversely bentaround the outside of said flange and yieldably secured thereto.

1 9. In a loudspeaker, in combination, a

chassis comprising a metal plate having a phragm having an annular rim of freely'flex-z horizontal base portion and a vertical face ible and inelasticmaterial, said rim-bein connected to the exterior of said cylindrica face to prevent slippage of air around the edge of said diaphragm.

6. In a loud speaker, in combination, a chassis comprising a metal plate having a horizontal baseportion and a vertical face portion, said face portion having an aperture therein to permlt free emission of sound waves therethrough, and having a rim-supporting portion in the form of a cylindrical trough, a diaphragm having an annular rim of freely flexible and inelastic material, driv, ing mechanism for said diaphragm positioned on said base portion, said rimbeing portion, said face portion having an aperture therein to permit free emission of sound waves therethrough, said face plate having an integral inwardly extending flared flange at'said'aperture, a diaphragm having an annular rim of freely flexible and inelastic material, driving-mechanism arranged to support and'drive said diaphragm positioned on said base portion, said rim being reversely bent around the outside of said flange, and

yieldably'secured thereto. v

Signed at Rochester in the county 'of Monroe and State of New Yorkthis 30th day of June, A. D. 1927.

IGOR S. BOBROVSKY; 

